CN108780915A - Lithium secondary battery with the lithium metal formed on anode and its manufacturing method - Google Patents

Abstract

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having lithium formed on a positive electrode side as a negative electrode active material. In the lithium secondary battery according to the present invention, coating is performed through the process of forming a lithium thin film on the negative electrode current collector while being isolated from the atmosphere, so that the oxide layer on the surface of the lithium metal caused by oxygen and moisture in the atmosphere can be suppressed formation, resulting in an effect of improving cycle life performance.

Description

Lithium secondary battery having lithium metal formed on positive electrode and manufacturing method thereof

technical field

This application claims priority and benefit from Korean Patent Application No. 10-2016-0089154 filed with the Korean Intellectual Property Office on July 14, 2016, the entire contents of which are incorporated herein by reference.

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having lithium metal formed on a positive electrode side, and a manufacturing method thereof.

Background technique

Various devices ranging from mobile phones, wireless electronic devices to electric vehicles that require batteries have been developed recently, and with the development of these devices, the demand for secondary batteries has also increased. In particular, as electronic products tend to become lighter, secondary batteries also tend to be lighter and smaller.

According to this trend, lithium secondary batteries using lithium metal as an active material are attracting attention. Lithium metal has a low redox potential (-3.045 V vs. standard hydrogen electrode) and high gravimetric energy density (3,860 mAhg ^-1 ), and is promising as an anode material for high-capacity batteries.

However, when lithium metal is used as the negative electrode of the battery, lithium foil is usually attached to a flat current collector to make the battery, and the disadvantage of lithium is that it is difficult to prepare and use in a general environment because lithium has a high reactivity as an alkali metal , thereby reacting explosively with water and also with atmospheric oxygen. In particular, _oxide layers such as _LiOH , _Li2O , and Li2CO3 are obtained due to oxidation when Li metal is exposed to the atmosphere. When there is a surface oxide layer (native layer) on the surface, the oxide layer acts as an insulating layer that reduces electrical conductivity, and suppresses smooth migration of lithium ions, increasing resistance.

For these reasons, a vacuum deposition process is performed when forming the lithium anode, and the problem of forming a surface oxide layer caused by the reactivity of lithium metal is partially ameliorated, however, lithium metal is still exposed to the atmosphere during the battery assembly process, and It is impossible to fundamentally suppress the formation of the surface oxide layer. In view of the above, there is a need to develop lithium metal electrodes that can solve the reactivity problem of lithium and simplify the process more while using lithium metal to improve energy efficiency.

[Prior art literature]

Korean Patent Application Publication No. 10-2016-0052323, "Lithium Electrode and Lithium Battery Including the Same (Lithium Electrode and Lithium Battery Including the Same)"

Contents of the invention

technical problem

As mentioned above, lithium secondary batteries are limited in the manufacturing process due to the reactivity of lithium metal, and when the battery is assembled, there is a problem of battery life and performance degradation due to inevitable contact with oxygen and moisture in the atmosphere. As a result of extensive studies, the inventors of the present invention have discovered a method of preventing contact with the atmosphere present when assembling a battery, and completed the present invention.

Accordingly, an aspect of the present invention provides a lithium secondary battery having enhanced performance and lifespan by blocking contact with the atmosphere during the formation of a lithium thin film of the lithium secondary battery.

Technical solutions

In view of the above, when a lithium secondary battery is assembled, the present invention manufactures the battery by laminating a lithium thin film on one side of the positive electrode mixture (not on the negative electrode current collector), and during the initial charging process of operating the battery afterwards, the layered The lithium pressed on the positive electrode mixture migrates to the negative electrode current collector in the form of lithium ions, so that lithium can be formed on the negative electrode current collector while being shielded from the atmosphere.

According to a first aspect of the present invention, there is provided a lithium secondary battery in which an anode mixture as lithium metal is separated from an anode current collector, is located between a cathode mixture and a separator, and is formed on one surface of the cathode mixture.

According to a second aspect of the present invention, there is provided a lithium secondary battery, wherein the negative electrode mixture as lithium metal is separated from the negative electrode current collector, is located between the positive electrode mixture and the separator, and is formed on one surface of the positive electrode mixture, and A polymer protective layer is formed between the negative electrode current collector and the separator.

Beneficial effect

In the lithium secondary battery according to the present invention, coating is performed through the process of forming a lithium thin film on the negative electrode current collector while being isolated from the atmosphere, and therefore, it is possible to suppress the lithium metal surface oxide caused by oxygen and moisture in the atmosphere The formation of the layer results in the effect of enhancing the cycle life performance.

Description of drawings

FIG. 1 is a schematic diagram of a lithium secondary battery manufactured according to a first embodiment of the present invention.

FIG. 2 is a simulation diagram showing the migration of lithium ions (Li ⁺ ) when the lithium secondary battery manufactured according to the first embodiment of the present invention is initially charged.

FIG. 3 is a simulation diagram of a lithium secondary battery manufactured according to the first embodiment of the present invention after initial charging is completed.

FIG. 4 is a simulation diagram of a lithium secondary battery manufactured according to a second embodiment of the present invention.

Detailed ways

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various forms and is not limited to this description.

In the drawings, in order to clearly describe the present invention, parts irrelevant to the description are not included, and the same reference numerals are used for the same elements throughout the specification. In addition, the sizes and relative sizes of constituent parts shown in the drawings do not relate to actual scales, and may be reduced or enlarged for clarity of description.

Fig. 1 is a simulation diagram of a lithium secondary battery manufactured according to the first embodiment of the present invention, and discloses a lithium secondary battery comprising: a positive electrode (10) comprising a positive electrode current collector (11 ) and positive electrode mixture (12); negative electrode (20), said negative electrode (20) comprises negative electrode current collector (21) and negative electrode mixture (22); The separator (30) that is arranged in between; And electrolyte (not shown), Wherein the negative electrode mixture (22) as lithium metal is separated from the negative electrode current collector (21), between the positive electrode mixture (12) and the separator (30), and is formed on one surface of the positive electrode mixture (12).

2 is a simulation diagram showing the migration of lithium ions (Li ⁺ ) when the lithium secondary battery manufactured according to the first embodiment of the present invention is initially charged, and FIG. 3 is the lithium secondary battery manufactured according to the first embodiment of the present invention at A mock-up after completing the initial charge.

When referring to Fig. 2 and Fig. 3, the present invention manufactures a battery by forming lithium used as a negative electrode active material of a lithium secondary battery on one surface of the positive electrode mixture (12) instead of the negative electrode current collector (21) metal (22), and then lithium ions migrate to the negative electrode side by initial charging when operating the battery, and a lithium thin film (22) is formed on the negative electrode current collector (21). More specifically, when the lithium thin film (22) as the negative electrode active material is formed on one surface of the positive electrode mixture (12), the lithium thin film (22) is formed on the negative electrode current collector (21) while being isolated from the atmosphere , and prevent the formation of an oxide layer on the lithium surface, thereby improving the life performance of the lithium secondary battery.

Lithium metal is preferably formed in a thin film on the positive electrode mixture (12), and the formation method is not particularly limited as long as it is a lamination or deposition process, and includes but is not limited to various deposition methods, such as electron beam deposition methods, Metalorganic chemical vapor deposition methods, reactive sputtering, high frequency sputtering and magnetron sputtering. Each of the illustrated deposition methods is a known method, and a detailed description thereof will not be included in this specification.

The lithium thin film (22) formed on one surface of the positive electrode mixture (12) can have its width adjusted according to the electrode shape in order to easily manufacture a battery, specifically, the thickness is preferably 1 μm to 100 μm. When the thickness is less than 1 μm, it is difficult to satisfy cycle properties due to insufficient lithium efficiency, and when the thickness is greater than 100 μm, there is a problem of decreased energy density due to increased lithium thickness.

The lithium secondary battery moves the lithium metal formed on the positive electrode mixture (12) to the negative electrode current collector in the form of lithium ions by applying an electric current before use, and forms a lithium film (22) coated on the negative electrode current collector (21). ) negative pole. Here, the initial charge is preferably performed by 1 to 2 charges and discharges at a current density of 0.01C to 0.5C because the shape of lithium metal formed on the negative electrode changes according to the initial charge current density.

4 is a simulation diagram of a lithium secondary battery according to a second embodiment of the present invention, and the present invention discloses a lithium secondary battery comprising: a positive electrode (10) comprising a positive electrode current collector ( 11) and positive electrode mixture (12); negative electrode (20), described negative electrode (20) comprises negative electrode current collector (21) and negative electrode mixture (22); The diaphragm (30) that is arranged in between; And electrolyte (not shown) , wherein the negative electrode mixture (22) as lithium metal is separated from the negative electrode current collector (21), and is located between the positive electrode mixture (12) and the separator (30), and is formed on one surface of the positive electrode mixture (12), and A polymer protective layer (40) is formed between the negative electrode current collector (21) and the separator (30).

The lithium thin film ( 22 ) of the second embodiment is the same as the lithium thin film ( 22 ) described above in the first embodiment, and description thereof will not be repeated.

The polymer protective layer (40) additionally introduced in the second embodiment is a lithium ion conducting polymer, for example, may be formed from any one or a mixture of two or more selected from the following: polycyclic Ethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), LiPON, Li ₃ N, Li _x La _1-x TiO ₃ (0<x<1) and Li ₂ S-GeS-Ga ₂ S ₃ , but not limited thereto, and polymers with lithium ion conductivity can be used without limitation things.

A polymer protective layer (40) having a smaller thickness is beneficial to battery output performance, however, the layer needs to be formed above a certain thickness in order to suppress a side reaction between lithium and the electrolyte formed later on the negative electrode current collector, and Effectively prevent dendrite growth. In the present invention, the polymer protective layer (40) may preferably have a thickness of 0.01 μm to 50 μm. When the thickness of the protective layer is less than 0.01 μm, the side reaction and exothermic reaction between lithium and the liquid electrolyte (which increase under overcharge and high-temperature storage conditions) cannot be effectively suppressed, and the safety cannot be improved sex. When the thickness is greater than 50 μm, it takes a long time for the polymer matrix in the protective layer to be impregnated or swelled by the liquid electrolyte, and the reduction of Li-ion migration leads to concerns about overall battery performance degradation. When considering the importance of the improvement effect obtained from the formation of the protective layer, the protective layer is more preferably formed to a thickness of 10 nm to 1 μm.

The polymer protective layer (40) can be prepared by coating or spraying a polymer composition (a mixture of an ion-conductive polymer and a solvent) on the negative electrode current collector (21), or dipping the negative electrode current collector (21) In the polymeric protective layer composition, the resultant is then dried. More specifically, after the polymer protective layer composition is dispersed in a solvent to prepare a slurry, the slurry may be coated on the negative electrode current collector (21).

The solvent used here preferably has a solubility index similar to that of the ion-conductive polymer (20), and preferably has a low boiling point. This is due to the fact that homogeneous mixing can be obtained and the solvent can be easily removed later. Specifically, N,N'-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone, tetrahydrofuran, dichloromethane, chloroform, dimethyl Methyl formamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water or mixtures thereof can be used as solvent.

A method of coating the prepared polymer protective layer composition on the negative electrode current collector (21) may be selected from known methods, or a new appropriate method may be used in consideration of material properties and the like. For example, the polymer protective layer composition is distributed on the negative electrode current collector (21), and then uniformly dispersed preferably using a spatula or the like. In some cases, methods that use distribution and dispersion steps in one process can also be used. In addition, methods such as dip coating, gravure coating, slot die coating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, and cap coating Available for preparation. Here, the negative electrode current collector (21) is the same as above.

Afterwards, the polymer protective layer (40) formed on the negative electrode current collector (21) can be subjected to a drying process, here, depending on the type of solvent used in the polymer protective layer composition, such as at 80° C. to 120 The drying process is carried out by heat treatment at a temperature of ℃ or hot air drying.

The configurations other than the lithium thin film or the polymer protective layer (40) of the lithium secondary battery of the first embodiment or the second embodiment can be prepared using known techniques implemented by those skilled in the art, which will be described in detail below. described structure.

The negative electrode current collector (21) according to the present invention is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and may be selected from copper, aluminum, stainless steel, zinc, titanium, silver, palladium, Any one of nickel, iron, chromium, its alloys and their combinations. The surface of stainless steel can be treated with carbon, nickel, titanium or silver, and aluminum-cadmium alloys can be used as alloys. In addition, roasted carbon, non-conductive polymers whose surfaces are treated with conductors, conductive polymers, etc. can be used. . As the negative electrode current collector, a copper thin plate is generally used.

The negative electrode current collector ( 21 ) can generally be prepared to have a thickness of 3 μm to 500 μm, and various forms such as film, sheet, foil, net, porous body, foam and non-woven fabric can be used.

The positive electrode mixture (12) according to the present invention can be prepared in a positive electrode form by film-forming a composition comprising a positive electrode active material, a conductor, and a binder on a positive electrode current collector.

As the positive electrode active material, one can use LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li( _Nia Co _b Mn _c )O ₂ (0<a<1, 0<b<1, 0<c <1, a+b+c=1), LiNi _1-y Co _y O ₂ , LiCo _1-y Mn _y O ₂ , LiNi _1-y Mn _y O ₂ (0≤y<1), Li(Ni _a Co _b Mn _c )O ₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn _2-z Ni _z O ₄ , LiMn _2-z Co _z Any one of O ₄ (0<z<2), LiCoPO ₄ and LiFePO ₄ , or a mixture of two or more thereof. In addition, in addition to these oxides, sulfides, selenides, halides, and the like can also be used. In a more preferable example, the cathode active material may be LiCoO ₂ suitable for high output batteries.

The conductor is a component for further improving the conductivity of the positive electrode active material, and non-limiting examples thereof may include: graphite, such as natural graphite or artificial graphite; carbon black-based materials, such as carbon black, acetylene black, Ketjen black, Channel black, furnace black, lamp black and thermal black; conductive polymers such as carbon or metal fibers; metal powders such as fluorocarbons, aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides, such as titanium oxide; conductive materials, such as polyphenylene derivatives, etc.

The binder has the effect of maintaining the positive electrode active material on the positive electrode current collector and organically connecting the positive electrode active material, examples of which may include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene Rubber, fluororubber, their various copolymers, etc.

The positive electrode current collector (11) is the same as described in the negative electrode current collector (21), and generally an aluminum thin plate can be used as the positive electrode current collector (11).

The separator (30) according to the present invention is not particularly limited in material, and as a material that physically separates the positive electrode (10) and the negative electrode (20) and has electrolyte and ion permeability, those materials that are generally used as separators in electrochemical devices Can be used without particular limitation. However, as porous, non-conductive and insulating materials, those having excellent liquid electrolyte moisture-holding capacity while having low resistance to ion migration of the liquid electrolyte are particularly preferred. For example, a polyolefin-based porous film or nonwoven fabric may be used, however, the separator is not particularly limited thereto.

As an example of a polyolefin-based porous film, a film formed using a single polyolefin-based polymer such as polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, etc., can be used. Ethylene and ultra-high molecular weight polyethylene, polypropylene, polybutene and polypentene, or polymers blending these polyolefin-based polymers.

As nonwoven fabrics other than the above-mentioned polyolefin-based nonwoven fabrics, nonwoven fabrics formed using polymers such as polyphenylene ether, polyimide, polyamide, polycarbonate, Polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyethersulfone, polyether ether ketone, polyester, etc. , or polymers in which these polymers are mixed, and, as the form of fibers forming a porous network, such nonwoven fabrics include spun-bonded or melt-blown forms formed with long fibers.

The thickness of the separator (30) is not particularly limited, but is preferably in the range of 1 μm to 100 μm, more preferably in the range of 5 μm to 50 μm. When the thickness of the separator is less than 1 μm, mechanical properties may not be maintained, and when the thickness is greater than 100 μm, the separator functions as a resistive layer, thereby degrading battery performance.

The pore diameter and porosity of the separator ( 30 ) are not particularly limited, however, the pore diameter is preferably 0.1 μm to 50 μm, and the porosity is preferably 10% to 95%. When the pore size of the separator is less than 0.1 μm or the porosity is less than 10%, the separator functions as a resistive layer, and when the pore size is greater than 50 μm or the porosity is greater than 95%, the mechanical properties may not be maintained.

The electrolyte that can be used in the present invention may be a non-aqueous liquid electrolyte or a solid electrolyte that does not react with lithium metal, but is preferably a non-aqueous electrolyte, and contains an electrolyte salt and an organic solvent.

The electrolyte salt contained in the nonaqueous liquid electrolytic solution is a lithium salt. As the lithium salt, those generally used in liquid electrolytes for lithium secondary batteries can be used without limitation. For example, the anion of the lithium salt may include F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , Any of (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- One, or two or more of them.

As the organic solvent contained in the nonaqueous liquid electrolytic solution, those organic solvents generally used in liquid electrolytes for lithium secondary batteries can be used without limitation, for example, ethers, esters, amides, linear carbonates, cyclic carbonic acids Esters and the like may be used alone or in admixture of two or more. Among them, generally, carbonate compounds that are cyclic carbonates, linear carbonates, or mixtures thereof can be included.

Specific examples of the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-butylene carbonate, Any one of pentyl ester, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and their halides, or a mixture of two or more thereof. Examples of the halide thereof may include fluoroethylene carbonate (FEC) and the like, but are not limited thereto.

Specific examples of the linear carbonate compound may generally include those selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethylene propyl carbonate. Any one of them, or a mixture of two or more of them, but not limited thereto.

In particular, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can more favorably dissociate lithium salts in electrolytes , and when mixed with this cyclic carbonate in an appropriate ratio and using linear carbonates with low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate, liquid electrolytes with higher conductivity can be prepared .

In addition, as the ether in the organic solvent, any one selected from dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether, or two of them can be used. A mixture of one or more, however, the ether is not limited thereto.

As the ester in the organic solvent, one selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, Any one of γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, however, the ester is not limited thereto.

Depending on the fabrication process and desired properties of the final product, the non-aqueous liquid electrolyte can be injected at an appropriate stage in the electrochemical device fabrication process. In other words, the non-aqueous liquid electrolyte can be injected at a stage before assembling the electrochemical device or at the final stage of assembling the electrochemical device.

In addition to winding as a general process, the lithium secondary battery according to the present invention may undergo lamination (stacking) and folding processes of separators and electrodes. In addition, the battery case may be cylindrical, square, pouch-shaped, coin-shaped, or the like.

The lithium secondary battery according to the first embodiment of the present invention can be manufactured by: i) forming a positive electrode mixture (12) on the positive electrode current collector (11); ii) forming a lithium thin film (22) on the positive electrode mixture (12); iii) successively disposing the separator (30) and the negative electrode current collector (21) on the lithium thin film (22), and then laminating the resultant; and iv) injecting the electrolyte.

The lithium secondary battery according to the second embodiment of the present invention can be manufactured by: i) forming a positive electrode mixture (12) on the positive electrode current collector (11); ii) forming a lithium thin film (22) on the positive electrode mixture (12); ii-1) forming a polymer protective layer (40) on the negative electrode current collector (21); iii) continuously setting the separator (30) and the negative electrode current collector with the polymer protective layer (40) on the lithium film (22) (21); and iv) injecting electrolyte.

The lithium secondary battery with the lithium thin film (22) formed on one surface of the positive electrode mixture (12) manufactured according to the present invention can laminate the lithium on the positive electrode mixture (12) on the negative electrode current collector (21) through initial charging . The thin film of lithium (22) moves through the electrolyte in the direction of the negative electrode in the form of lithium ions (Li ⁺ ), and is precipitated and laminated on the negative electrode current collector (21) as lithium metal. In addition, in the lithium secondary battery manufactured according to the second embodiment of the present invention, lithium metal is laminated between the negative electrode current collector (21) and the polymer protective layer (40) during initial charging.

preferred embodiment

Hereinafter, the present invention will be described in detail with reference to Examples. However, the embodiments according to the present invention can be modified into various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The examples of the present invention are provided to more fully describe the present invention to those of ordinary skill in the art.

[Example 1]

The LCO-based positive active material, Super-P (conductive carbon black) and PVdF were mixed at a weight ratio of 95:2.5:2.5, and then coated on an aluminum current collector to form a positive electrode (loading 450 mg/25 cm ² ). Lithium metal with a thickness of 20 μm was laminated thereon using a lamination method.

On one surface of the copper current collector, a negative electrode formed with a 0.2 μm thick LiPON protective layer was prepared.

A porous polyethylene separator was provided between the prepared positive and negative electrodes to prepare an electrode assembly, and after the electrode assembly was placed in a case, an electrolyte was injected thereinto to manufacture a lithium secondary battery. Here, the electrolyte was prepared by dissolving 1M LiPF ₆ and 2% by weight vinylene carbonate (VC) in fluoroethylene carbonate (FEC) at a volume ratio of 1:1:2:1. : Ethylene carbonate (EC): Diethyl carbonate (DEC): Dimethyl carbonate (DMC) in an organic solvent.

[Example 2]

A lithium secondary battery was manufactured in the same manner as in Example 1 except that no LiPON protective layer was formed in the negative electrode.

[Example 3]

A lithium secondary battery was manufactured in the same manner as in Example 1, except that a 0.3 μm thick PVdF-HFP (HFP content: 5% by weight) protective layer was formed on one surface of the copper current collector instead of the negative electrode LiPON protection layer in.

[Comparative example 1]

A lithium secondary battery was fabricated in the same manner as in Example 1, except that lithium metal was not laminated in the positive electrode, 20 μm thick lithium metal was laminated on one surface of the copper current collector, and a LiPON protective layer was not formed.

[Experimental example 1]

For the lithium secondary batteries manufactured in Example 1 and Comparative Example 1, charging and discharging were performed under the conditions of charging at 0.2C, 4.25V CC/CV (5% current cutoff at 1C) and discharging at 0.5C CC 3V Tested, and the number of cycles to reach 80% capacity relative to initial capacity is recorded in Table 1 below.

[Table 1]

Number of cycles at 80% capacity relative to initial capacity Example 1 230 Comparative example 1 130

The test results showed that compared with the lithium secondary battery of Comparative Example 1, the life performance of the lithium secondary battery of Example 1 was improved by about 1.77 times, and it was seen that this was suppressed by preventing lithium from being exposed to the atmosphere during the manufacturing process. The surface oxide layer and the effect obtained by the polymer protective layer on the negative current collector.

[Experimental example 2]

For the lithium secondary batteries manufactured in Examples 1 to 3, after charging at 0.03C, 4.25V CC/CV (5% current cut-off at 1C), then discharging at 0.5C CC 3V and at 0.2C, 4.25V CC Charge and discharge tests were performed under the condition of /CV (5% current cutoff at 1C) charge, and the number of cycles to reach 80% capacity relative to the initial capacity is recorded in Table 2 below.

[Table 2]

Number of cycles at 80% capacity relative to initial capacity Example 1 350 Example 2 275 Example 3 332

This test is to demonstrate the effect of the polymer protection layer, and when comparing Example 1 with LiPON protection layer, Example 2 without polymer protection layer and Example 3 with PVdF-HFP protection layer, with polymer The life performance of the battery of the protective layer was excellent, and in particular, it was confirmed that the LiPON protective layer further improved the life performance compared with the PVdF-HFP protective layer.

In addition, it was confirmed that when the initial charging was performed at a current density lower than that of Experimental Example 1, the life performance was further improved, and it can be seen that this is attributable to the plate shape of the lithium metal initially formed on the negative electrode, and the thin and firm formation The SEI layer.

Industrial Applicability

The lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output performance and capacity retention rate, and therefore, can be used in portable devices such as mobile phones, notebook computers or digital cameras, such as hybrid electric vehicles (HEV) fields such as electric vehicles.

Accordingly, another embodiment of the present invention provides a battery module including a lithium secondary battery as a unit cell, and a battery pack including the battery module. The battery module or battery pack may be used as a power source for any one or more medium to large devices selected from: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrids Propulsion electric vehicles (PHEV); or power storage systems.

Claims (11)

1. a kind of lithium secondary battery, it includes：

Anode, the anode include anode current collector and cathode mix；

Cathode, the cathode include negative electrode current collector and negative electrode mix；

The diaphragm being disposed there between；With

Electrolyte,

The wherein described negative electrode mix is arranged between the diaphragm and the cathode mix to be formed by being charged and discharged Lithium film.

2. lithium secondary battery according to claim 1, wherein the negative electrode mix passes through 1 to 2 at 0.01C to 0.5C Secondary charging and discharging are formed in the lithium form of film in the negative electrode current collector.

3. lithium secondary battery according to claim 1, wherein the negative electrode mix has 1 μm to 100 μm of thickness.

4. lithium secondary battery according to claim 1, wherein the cathode mix include positive electrode active materials, conductor and Adhesive.

5. lithium secondary battery according to claim 4, wherein the positive electrode active materials are selected from：LiCoO₂、LiNiO₂、 LiMnO₂、LiMn₂O₄、Li(Ni_aCo_bMn_c)O₂(0<a<1,0<b<1,0<c<1, a+b+c=1), LiNi_1-yCo_yO₂、LiCo_{1- y}Mn_yO₂、LiNi_1-yMn_yO₂(0≤y<1)、Li(Ni_aCo_bMn_c)O₄(0<a<2,0<b<2,0<c<2, a+b+c=2), LiMn_{2- z}Ni_zO₄、LiMn_2-zCo_zO₄(0<z<2)、LiCoPO₄、LiFePO₄And combination thereof.

6. lithium secondary battery according to claim 1, wherein being formed between the negative electrode current collector and the diaphragm poly- Close object protective layer.

7. lithium secondary battery according to claim 6, wherein the polymer protective layer is by lithium-ion-conducting polymer It is formed.

8. lithium secondary battery according to claim 6, wherein the polymer protective layer is selected from：Polyethylene oxide (PEO), Polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropene (PVDF-HFP)、LiPON、Li₃N、Li_xLa_1-xTiO₃(0<x<And Li 1)₂S-GeS-Ga₂S₃。

9. lithium secondary battery according to claim 6, wherein the polymer protective layer has 0.01 μm to 50 μm of thickness Degree.

10. a kind of method of manufacture lithium secondary battery comprising：

I) cathode mix is formed in anode current collector；

Ii) negative electrode mix is formed on the cathode mix；

Iii) diaphragm and negative electrode current collector on the negative electrode mix are continuously set, gains are then laminated；And

Iv electrolyte) is injected,

Wherein, before using the battery, lithium film is formed by being charged and discharged in the negative electrode current collector.

11. it is according to claim 10 manufacture lithium secondary battery method, in ii) and iii) between further include, described Polymer protective layer is formed in negative electrode current collector.